<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <meta http-equiv="X-UA-Compatible" content="ie=edge">
    <title>Document</title>
    <link rel="stylesheet" href="./css/reset.min.css">
    <style>
        .red {
            background: red
        }
    </style>
</head>

<body>
    <ul>
        <li class="demo demo1 ">1</li>
        <li>2</li>
        <li>3</li>
        <li>4</li>
    </ul>
</body>
<!-- <script src="./js/utils.js"></script> -->
<script src="./js/jquery1.11.3.js"></script>
<script>

    $(function () {
        $('ul li').eq(0).addClass('red')
        $('ul li').eq(0).removeClass('demo')
        
    })


</script>

</html>